XRRScreenSize structure contains a possible root size in pixels and in
millimeters. XRRScreenChangeNotifyEvent Is sent to a client that has requested
notification whenever the screen configuration is changed.

XRRScreenConfiguration
This is an opaque data type containing the configuration information for
a screen.

Timestamps

Time stamps are included and must be used to ensure
the client is playing with a full deck: the screen may change properties
on the fly and this ensures its knowledge of the configuration is up to
date. This is to help issues when screens may become hot-pluggable in the
future.

Xrandr is a simple library designed to interface the
X Resize and Rotate Extension. This allows clients to change the size and
rotation of the root window of a screen, along with the ability to reflect
the screen about either axis (if supported by the implementation). Rotation
and reflection may be implemented by software and may result in slower
performance if rotation and reflection are implemented in this fashion
(as are all implementations as of October 2002).

The Xrandr library does
some minimal caching to avoid roundtrips to provide clients frequently
used information. See "The X Resize and Rotate Extension" for a detailed
description; also note that depth switching, as described in the document
is not implemented, and may (or may not) ever be implemented, as display
memory is growing rapidly, and toolkits are already beginning to support
migration, mitigating the need for depth switching. If it is implemented
in the future, we expect to do so via an upward compatible extension to
the current library/protocol; functionality described here should continue
to work.

Rotation and reflection and how they interact can be confusing.
In Randr, the coordinate system is rotated in a counter-clockwise direction
relative to the normal orientation. Reflection is along the window system
coordinate system, not the physical screen X and Y axis, so that rotation
and reflection do not interact. The other way to consider reflection is
to is specified in the "normal" orientation, before rotation, if you find
the other way confusing.

The XRRScreenChangeNotify event is sent to clients
that ask to be informed whenever the root window configuration changes.
Configuration changes may include resolution, physical size, subpixel
order (see XRender(3)
), and rotation. Note that changes to any or all of
these could occur due to external events (user control in the X server,
a different monitor/flat panel display being hot-plugged) and is not only
the result of a protocol/library request to the X server.

Additionally,
to eliminate a potential race condition, this event may be generated immediately
upon selecting for notification if the screen has changed since the client
of Xrandr connected to the X server, to enable reliable screen resolution
changing when a user may log in and change the configuration while one
or many clients are starting up.

Xlib notification

Clients must call back
into Xlib using XRRUpdateConfiguration when screen configuration change
notify events are generated (or root window configuration changes occur,
to update Xlib's view of the resolution, size, rotation, reflection or subpixel
order. Generally, toolkits will perform this operation on behalf of applications;
we did not want to change display structure data behind the back of toolkits,
as in multithreaded clients, various race conditions might occur. Toolkits
should provide clients some mechanism for notification of screen change,
of course.

There are two classes of interfaces: those which can
be safely called even if RandR is not implemented on a screen (to make
common idioms not dependent on the server having support), and those which
will return errors if the extension is not present.

XRRRotations returns
both the possible set of rotations/reflections supported (as a bitmask)
as the value of the function, along with the current rotation/reflection
of the screen.

XRRSizes returns the size and a pointer to the current sizes
supported by the specified screen. The first size specified is the default
size of the server. If RandR is not supported, it returns 0 for the number
of sizes.

XRRRates returns a pointer to a the rates supported by the specified
size. If RandR is not supported, it returns 0 for the number of rates.

XRRTimes
returns the time last reported by the server along with the timestamp the
last configuration changed. If the configuration has changed since the client
last updated its view of the server time, requests to change the configuration
will fail until the client has an up to date timestamp.

XRRRootToScreen
returns the screen number given a root window (for example, from an XRRScreenChangeNotifyEvent.

The rest of the functions will fail if applied to screens not implementing
the RandR extension. XRRSetScreenConfig sets the screen size and rotation
and reflection to the desired values on the screen specified by draw, or
returns a BadValue error. size_index specifies which size configuration
is to be used, rotation specifies which rotation or reflection is to be
used (or a BadValue error is returned). The timestamp is used by the server
to make sure the client has up to date configuration information. Status
is returned to indicate success or failure; a client must refresh its configuration
information if it fails and try the call again (by calling XRRGetScreenInfo).

XRRSetScreenConfigAndRate like XRRSetScreenConfig but also set the refresh
rate. If specified rate is not supported a BadValue error is returned.

XRRConfigRotations,XRRConfigSizes,XRRConfigCurrentConfiguration,XRRConfigTimes,XRRConfigRates,
and XRRConfigCurrentRate are used to get specific configuration information
out of a screen configuration.

XRRGetScreenInfo Returns a screen configuration
for later use; the information is private to the library. Call XRRFreeScreenConfigInfo
to free this information when you are finished with it. It forces a round
trip to the server.

Other functions include: XRRQueryExtension which returns
the event and error base codes, XRRQueryVersion , which returns the current
version of the extension (this information is cached by the library).